Two weeks later Aidan fell ill with flu-like symptoms and within two days he was dead.

Aidan's family claim Petco knew of the "hidden dangers" because there had been more than a dozen cases of adults and children contracting rat-bite fever from animals sold by the US chain since 2001.

Family lawyer Bibianne Fell told a court: “Despite this, you will hear that Petco is still selling rats to kids and kids are still getting sick.”

The bacterial disease leads to a rash and swelling, vomiting, headaches and fever, and can be fatal if not treated with antibiotics.

The company is fighting the claim, insisting it cannot possibly ensure the millions of rodents it sells are free of bacteria and customers are warned of the risk of infection in paperwork on how to care for rats.

MOST READ IN NEWS

INK AGAIN

Tattoo disasters that left their embarrassed owners cringing with remorse

There may also be swollen joints and a rash over the hands and feet, identified by flat reddened areas with small bumps.

Spirillary rat-bite fever, also caled sodoku in Japan, is similar but has a longer incubation period of up to four weeks and the fever can recur for months. Symptoms can include an ulcer near the bite wound.

The North American disease is known as Haverhill fever when contracted from infected food or drink.

Antibiotics are highly effective at treating both kinds of rat-bite fever.

If not treated it can lead to serious infections of the heart, brain and lungs or septic shock, which can be fatal.

Source: Centers for Disease Control and Prevention

Aidan's dad Andrew Pankey has said previously: "I’m fighting this case to protect some children because I don’t want this to happen to another family.

"I still talk to him, tell him I love him, that daddy is not going to give up."